I always start the same way: let the FB print air dry, but not bone-dry.

First method I tried was to use a clothes iron. By sandwiching the print between two sheets of watercolor paper, I could "iron" the print to dryness and reasonable flatness. On the plus side, it's manual labour, which can help to free your mind from worries. On the minus side, you'll spend forever drying your prints if you have a stack of them.

Now what I do is simply put the prints between sheets of acid-free blotting paper, and put a few books on top of them. Every once in a while, I let the prints air a little bit, then it's back to the blotters. Eventually the prints are pleasantly dry and flat, after a day or two. But they will always curl a little bit no matter what, unless you mount them.

The paper brand makes a huge difference. Anything remotely Eastern European will curl a lot, whereas Ilford and Kentmere stay flat even without any pressure.